Papermaking machines consist of several sections such as the fourdrinier, press section, dryer sections, calendar section, a reel, as well as other sections that may be unique to a particular type or grade of paper being produced. Many of these sections consist of multiple rolls or "cans" over which the paper travels. To start a new paper sheet or web through the papermaking machine, ropes can be used to carry a narrow leading edge of the web of paper, commonly referred to as a "tail" through the rollers. At a junction of two sections, the tail must be transferred from one set of ropes to another. This procedure is illustrated in FIGS. 1-3.
Specifically, FIG. 1 is a top plan view of two adjacent dryer sections 10, 12 of a papermaking machine 14. To feed the new paper web 16 through the dryer sections 10, 12, the web 16 is provided with a tail 18 or a narrow leading edge as illustrated. The tail is inserted between two endless ropes 20, 22 that are wrapped partially around sheaves disposed at the ends of the dryer cans 24, 26 as well as the sheaves 28, 30 as shown in FIGS. 1 and 3. The upstream endless ropes 20, 22 must carry the tail 18 to the nip 32 formed by the two endless ropes 34, 36 that extend around the sheaves 38, 40, 42 as well as sheaves mounted at the ends of the dryer cans 44, 46 as also shown in FIGS. 1 and 3. Not shown in FIGS. 1 and 3 are stretching apparatuses used to adjust the tension of the endless ropes 20, 22 and 34, 36. Such stretching apparatuses are known in the art. Examples of such stretching apparatuses appear in U.S. Pat. Nos. 5,263,623, 5,375,753, 5,377,892 and 5,379,932. The sheaves mounted to the ends of the cans 24, 26, 44, 46 are also not shown but such sheaves are known in the art and are mounted to the can or roll head and rotate with the can or roll. The flow of the paper web 16 is illustrated in FIG. 2.
It will be noted that the downstream section 12 (cans 44, 46) can be operated at a higher speed than the upstream section (cans 24, 26) to apply an appropriate tension to the paper web 16.
The primary disadvantage with the tail transfer system illustrated in FIGS. 1-3 is the premature release of the tail 18 by the ropes 20, 22. Specifically, referring to FIG. 3, the ropes 20, 22 separate or diverge prior to reaching the nip 32 or the can 44. As a result, the tail 18 is released too early and towards the inside or the center of the papermaking machine before the downstream ropes 34, 36 form the nip 32 and can carry the tail 18 further downstream past the cans 44, 46.
As a result, there is a need for an improved web threading apparatus and method which does not result in a high incidence of the tail being released prematurely by the upstream ropes prior to the formation of the nip by the downstream ropes or a premature release by the upstream ropes which results in the tail being released inside towards the center of the papermaking machine.